Comparative Review of Two Different Design Approaches for SMA Based Continuum Robots

Abstract

Abstract Inspired by nature, the field of continuum robotics focuses on the research and development of bending and soft robotic structures. Like elephant trunks or tentacles, these robots are not based on discrete joints and rigid connecting structures, but exploit flexible bending motion with a high number of degrees of freedom. Because of a variety of possible fields of applications, continuum robots have experienced a strong increase in research interest within the last years. Possible applications range from medical (surgery) instruments over industrial inspection systems to soft and thus safe collaborative robotic structures for human-machine-interaction. Common actuation techniques applied in continuum robotic systems make use of conventional drive units, which are bulky, heavy and oftentimes stationary. An alternative to these conventional drives is the implementation of shape memory alloy (SMA) wire actuators as artificial metal muscles. Like muscle contraction, SMA wires contract at a specific phase transformation temperature due to a reversible phase transformation from a low temperature phase, called martensite, to a high temperature phase, austenite. This paper presents two specific design schemes for continuum robots based on SMA wire actuators. A first design is focused on maximum bending angles and range of motion. To reach this goal, the total maximum wire contraction is key. A Bowden cable inspired robot design is developed, which enables 3D motion and validated bending angles of over 200°. Because of the Bowden cable approach, the overall (passive) length of the robot is much longer than the actual actively bending tip of the robot [1], [2]. The second design approach is focused on a fully integrated continuum robot, including the integration of the SMA wires as well as the electrical wiring into the bending structure. Here, no additional passive part is required to exploit the movement of the continuum robot [3]. The design of the trunk-like structure as well as the wiring strategy are presented. Subsequently, the performance of both approaches is compared to each other. The study highlights advantages of either approach and enables application-specific design of SMA wire based continuum robot structures and complete systems. Possible applications are endoscopes with integrated camera systems for inspection tasks or possible handling systems for complex material handling tasks.